Search Results

Biodiesel has been paid more and more attention as a renewable fuel due to some excellent properties such as renewable, high cetane number, ultralow sulfur content, no aromatic hydrocarbon, high flash point, low CO2 emission when compared with diesel. While others physical properties like high viscosity, high surface tension, big density and bad volatility would spoil the spray characteristics of biodiesel fuel, which will affect the thermal efficiency when running in diesel engine. Accompanied with constant volume vessel and high speed video camera system, a high pressure common rail system, which could provide an injection pressure of 180 MPa, is used to investigate the characteristics of jatropha curcas biodiesel, palm oil biodiesel and diesel fuel. The effects of injection pressures and ambient densities on spray characteristics of these fuels are studied.

Gasoline homogeneous charge compression ignition (HCCI) can achieve high efficiency and extremely low NOX emissions. However, the working condition range of HCCI is limited by knock occurring during engine operation. To achieve an expanded HCCI working condition range, it is necessary to explore a method predicting knock cases accurately to avoid knock occurring. Based on a DI-HCCI engine with ethanol/gasoline mixed fuel, the knock cases under different conditions have been investigated. In-cylinder pressure signals are used to identify the knock cases and the knock oscillations are extracted with fast Fourier transform (FFT). The effects of the ethanol proportion in the fuel and air/fuel ratio on the characteristics of knock have been studied. The results have shown that the knock parameters, such as maximum frequency, start point angle and the duration, have close relationship with the knock intensity.

Pre-ignition may lead to an extreme knock (super-knock or mega-knock) which will impose a severe negative influence on the engine performance and service life, thus limiting the development of downsizing gasoline direct injection (GDI) engine. More and more studies reveal that the auto-ignition of lubricants is the potential source for pre-ignition. However, pre-ignition is complicated to study on the engine test bench. In this paper, a convenient test method is applied to investigate the influence of lubricants metal-additives on pre-ignition. 8 groups of lubricants are injected into a hot co-flow atmosphere which generated by a burner. A single-hole nozzle injector with a diameter of 0.2 mm at 20 MPa injection pressure is utilized for lubricants' injection and spray atomization. The ignition delays of lubricants with different additives of calcium, ZDDP (Zinc Dialkyl Dithiophosphates) and magnesium content under the hot co-flow atmosphere are recorded with a high-speed camera.

In this paper comparisons were made between the fuel economy improvement between a High Pressure loop (HP) water-cooled Exhaust Gas Recirculation (EGR) system and a Low Pressure loop (LP) water-cooled EGR system. Experiments were implemented on a 1.3-Litre turbocharged PFI gasoline engine in two pars. One was EGR rate as single operating point to compare the different effect of HP- and LP-EGR. The other was mini map from 1500rpm to 3000rpm and BMEP from 2bar to 14bar because of the relative narrow available range of HP-EGR system. In consideration of practical application of EGR system, the coolant used in this experiment was kept almost the same temperature as in real vehicles (88±3°C) instead of underground water temperature, besides a model was built to calculate constant volume ratio (CVR). The results indicated that the effect of HP-EGR was weaker than that of LP-EGR under the same EGR rate, which could be seen from change of combustion parameters.

Spray behavior is regarded as one of main factors which influence engine performance, fuel consumption and emissions for diesel engine. In practice, spray characteristics from each orifice from a multi-hole nozzle are normally arranged symmetrically, while the hole-to-hole spray variation is unavoidable. This variation will cause spatial uneven distribution of spray and combustion degrade, which will be no longer inconsiderable in face of the more and more stringent emission rules. In this paper, two methods including spray macro-characteristics experiment and separated fuel mass measurement are employed to test the hole-to-hole spray variation of two six-hole symmetric VCO injectors of different brands, and experiments are operated under different conditions including different injection pressures, back pressures and injection durations.